Epicyclic transmission for zero turning radius vehicles

ABSTRACT

A drive shaft rotated by a drive gear is coupled to an epicyclic gear arrangement which is rotatable as a unit about the drive shaft&#39;s longitudinal axis, as well as about its own axis. A driven gear is rotatably mounted on the on the drive shaft between the drive gear and the gear arrangement. Facing surfaces of the drive and driven gears are provided with annular concavities. A pivotally adjustable friction disk extends between, and in contact with, the concave surfaces. The opposite side of the driven gear is operatively connected to the gear arrangement. When the drive shaft is rotated, the gear arrangement is rotated about its own axis in response to drive shaft rotation and is rotated about the drive shaft&#39;s axis in accordance with the position of the friction disk. The speed and direction of the wheel-driving output are thus controlled.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an epicyclic transmissionparticularly suited for driving zero turning radius vehicles.

[0003] 2. Prior Art

[0004] Steering control for numerous vehicles depends on the differenceof speed which can be obtained between two drive wheels. When turning,the inner wheel rotates more slowly than the outer wheel. Vehicles thatcan turn about a point midway between the two drive wheels areclassified as zero turning radius (ZTR) vehicles. Such turning isaccomplished by one drive wheel rotating in a forward direction as fastas the other drive wheel rotates in the reverse direction.

[0005] A commonly used arrangement for achieving a zero turning radiusis employing a hydraulic motor and an associated vehicle displacementpump for hydraulically driving each wheel of a ZTR vehicle, such as ariding-type lawn tractor. However, hydraulic systems have disadvantagessuch as flow problems and leakage loss which affect efficiency. Also,pressure pulses can occur in hydraulic systems causing noise.

SUMMARY OF THE INVENTION

[0006] The present invention overcomes the above-noted deficienciesresulting in a quiet transmission not requiring the precision componentsnecessary for a hydraulic system.

[0007] The invention is an epicyclic transmission capable of use in azero turning radius vehicle. A drive shaft is coupled to a wheel-drivingoutput through an epicyclic gear arrangement which, as a unit, iscapable of rotation about a longitudinal axis of the drive shaft whilealso rotating about its own axis which extends transverse to the driveshaft's axis. A drive gear is joined to the drive shaft for rotationtherewith. A driven gear is mounted on the drive shaft but is rotatableindependently of the shaft's rotation. The driven gear is operativelyjoined to the epicyclic gear arrangement. Facing surfaces of the driveand driven gears are provided with annular concavities. A friction diskextends between the concave surfaces of the facing gears. The disk ispivotally adjustable so as to adjust the locations along the concavesurfaces which are engaged by the disk. Rotation of the drive gear istranslated by the disk to control the speed and the direction ofrotation of the driven gear dependent on the disk's position. When thedriven gear is rotated at a different speed than the drive gear, thedriven gear imparts forces on the epicyclic gear causing it to rotateabout the drive shaft's axis at the same time the epicyclic gear rotatesabout its own axis. Such compound movement of the epicyclic gear permitsthe speed and direction of the wheel-driving output to be controlled asa function of the position of the friction disk.

BRIEF DESCRIPTION OF THE DRAWING

[0008] The invention now will be described in greater detail withrespect to the accompanying drawing which represents a cross-sectionalview of a preferred embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0009] Referring now to the drawing, a central drive shaft 10 isprovided at its opposite ends with bevel gears 12 and 14 having toothedsurfaces 16 and 18, respectively. A drive gear 20 is secured to shaft 10intermediate its ends. Gear 20 is driven by a powered input (not shown)for rotation of the shaft 10 and the bevel gears 12 and 14.

[0010] Near each end of shaft 10, in positions adjacent gears 12 and 14,bearings 22 and 24 are provided. The bearing 22 rotatably supports theends of axially aligned pinion gears 26 and 28. Similarly, bearing 24supports correspondingly arranged pinion gears 30 and 32. Gears 26 and28 engage the teeth provided on the surface 16 of bevel gear 12, whilegears 30 and 32 engage the teeth on surface 18 of bevel gear 14.

[0011] Each of the pinion gears is further supported by a respectiveconcentrically arranged connector pin, the pins each comprising a shaftportion and a head. The shaft portions of pins 34, 36, 38 and 40 areretained within bearings in their respective pinion gears so that thepinion gears can rotate relative to their associated pins. Thebearing-retained shaft portion of pin 34 supports pinion gear 26; thatof pin 36 supports pinion gear 28; that of pin 38 supports pinion gear30; and that of pin 40 supports pinion gear 32. The heads of pins 34 and36 are secured to a cup-shaped drive cup 42 which is concentricallyaligned with the longitudinal axis of drive shaft 10. A stub shaft 44projecting from drive cup 42 is joined to a drive wheel (not shown) of avehicle. Similarly, another drive cup 46 provided at the opposite end ofshaft 10 is secured to the head portions of pins 38 and 40. Drive cup 46also has a projecting stub shaft 48. Shaft 48 is connected to a seconddrive wheel (not shown) of the vehicle.

[0012] On opposite sides of drive gear 20, driven gears 50 and 52 aresecured to bearings mounted on drive shaft 10. Thus, gears 50 and 52 arerotatable relative to shaft 10. The gears 50 and 52 are each providedwith a toothed surface. The toothed surface of gear 50 engages the teethof pinion gears 26 and 28, and the toothed surface of gear 52 engagesthe teeth of pinion gears 30 and 32.

[0013] A concave annular surface 54 is provided on one side of drivegear 20. The surface of driven gear 50 facing the drive gear 20 also isprovided with an annular concavity 56. A bearing support 58 ispositioned between gears 20 and 50. A friction disk 60 is pivotallyconnected to support 58 so as to extend in contacting relationshipbetween surfaces 54 and 56. An operator control (not shown) is joined todisk 60 so as to locate the edge of the disk in contacting relationshipwith the concave surfaces 54 and 56 at desired positions.

[0014] A similar arrangement is provided between drive gear 20 anddriven gear 52. Gears 20 and 52 are provided with facing annular concavesurfaces 62 and 64 between which a friction disk 66 extends, the diskbeing pivotally connected to a further bearing support 68 positionedbetween gears 20 and 52. As in the case of disk 60, disk 66 is joined toan operator control (not shown) so that the location where the disk'sedge contacts the concave surfaces of gears 20 and 52 can be selected.

[0015] The purpose of the friction disks will be described with respectto the arrangement of disk 60 between drive gear 20 and driven gear 50.It will be understood that this description also is applicable to thedisk 66 associated with gears 20 and 52.

[0016] With the disk 60 disposed in a plane parallel to the longitudinalaxis of the drive shaft 10, drive gear 20, driven gear 50 and bevel gear12 are rotated at the same speed. However, gears 50 and 12 rotate inopposite directions. Since gears 50 and 12 are positioned on oppositesides of pinion gears 26 and 28, the pinion gears merely rotate abouttheir common rotational axis which remains stationary. Thus, drive cup42 is not rotated, and no rotation is imparted to the first drive wheel.However, as disk 60 is pivoted so that its plane is angularly related tothe drive shaft's longitudinal axis, the relative speed between drivegear 20 and driven gear 50 changes. Depending on the direction anddegree of pivoting of the disk relative to the drive shaft'slongitudinal axis, the driven gear 50 is rotated either faster or slowerthan the drive gear at the same time that the bevel gear 12 is beingrotated by drive shaft 10 at the same speed and in the same direction asthe drive gear 20. The differences in speed and direction of rotation ofbevel gear 12 and the driven gear 50 result in forces being applied tothe pinion gears 26 and 28 causing them to rotate as a unit about theaxis of drive shaft 10 at the same time they are rotating about theirown axes. This movement is translated to the stub shaft 44 so as tocause the speed and direction of the vehicle's first drive wheel to becontrolled as a function of the position of disk 60.

[0017] When both disks 60 and 66 are appropriately manipulated by anoperator, the respective drive wheels of the vehicle can be rotated atdifferent speeds and in different directions. This capability permitsthe vehicle to be driven with a zero turning radius.

[0018] Although the embodiment which has been described with respect toits use with a zero turning radius vehicle, it will be understood thatit can be used in other types of vehicles where it is desirous to rotatethe drive wheels at different speeds and/or direction.

[0019] The embodiment described above employs a single drive shaft 10with duplicate arrays of components provided on opposite sides of adrive gear to achieve the desired results. However, it is apparent thatsuch an arrangement could be split into two transmissions utilizing aseparate drive shaft for each wheel. Also, instead of using piniongears, it is possible to employ planetary differential gearing.

What is claimed is:
 1. An epicyclic transmission for controlling thespeed and direction of rotation of a vehicle wheel, comprising: a driveshaft having an axis of rotation; a drive gear joined to the drive shaftfor imparting rotation to the drive shaft about said axis; a geararrangement mounted on the drive shaft, said gear arrangement beingrotatable about both the axis of rotation of the drive shaft and aboutits own rotational axis; a driven gear mounted on the drive shaftbetween said drive gear and the gear arrangement in operativerelationship with the gear arrangement, said driven gear being rotatableabout said axis of rotation of the drive shaft independently of rotationof the drive shaft, said drive and driven gears having surfaces facingone another provided with respective concavities therein; a pivotallyadjustable disk having an edge contacting the drive and driven gearswithin the concavities for controlling the speed and direction ofrotation of the driven gear in accordance with the position of the disk;an additional gear joined to the drive shaft for rotation therewith,said additional gear being positioned in operational relationship withthe gear arrangement on an opposite side of the gear arrangement fromthe driven gear; and a wheel-driving output element operatively engagedwith the gear arrangement.
 2. A transmission according to claim 1,wherein said gear arrangement comprises at least two gears radiallydisposed relative to the axis of rotation of the drive shaft.
 3. Atransmission according to claim 2, wherein said at least two gears arepinion gears.
 4. A transmission according to claim 2, wherein saidwheel-driving output comprises a gear which engages the said geararrangement.
 5. A transmission according to claim 2, further comprisinga connector element associated with each of said at least two gears,said connector element being joined to the wheel-driving output elementto translate rotation of the gear arrangement about the axis of rotationof the drive shaft to rotation of the wheel-driving element.
 6. Atransmission according to claim 5, wherein said at least two gears arepinion gears and wherein said connector elements are pins each having ashaft positioned along a respective axis of rotation of said at leasttwo gears, the said at least two gears being rotatable about theirrespective pin shafts.
 7. A transmission according to claim 2, whereinsaid driven gear includes teeth arranged to cooperate with teethprovided in said gear arrangement.
 8. A transmission according to claim7, wherein said teeth are located on an opposite side of the driven gearfrom the surface in which said annular concavity is provided.
 9. Atransmission according to claim 1, wherein when said disk is positionedin a plane parallel to the axis of rotation of the drive shaft, the geararrangement rotates only about its rotational axis.
 10. A transmissionaccording to claim 1, wherein when said disk contacts the drive gear ata location closer to the axis of rotation of the drive shaft than wherethe disk contacts the driven shaft, the gear arrangement rotates aboutthe axis of rotation of the drive shaft in a first direction as well asabout its rotational axis, and wherein when said disk is in a positionin which the disk contacts the drive gear at a location farther awayfrom the axis of rotation of the drive shaft than where the diskcontacts the driven shaft, the gear arrangement rotates about the axisof rotation of the drive shaft in an opposite direction as well as aboutits rotational axis.
 11. A transmission according to claim 1, whereinsaid gear arrangement is a pinion gear.
 12. A transmission according toclaim 1, wherein said wheel-driving output comprises a gear whichengages the gear arrangement.
 13. A transmission according to claim 1,further comprising a connector element associated with said geararrangement, said connector element being joined to the wheel-drivingoutput element to translate rotation of the gear arrangement about theaxis of rotation of the drive shaft to rotation of the wheel-drivingelement.
 14. A transmission according to claim 13, wherein said geararrangement is a pinion gear and wherein said connector element is a pinhaving a shaft positioned along the rotational axis of said geararrangement, the gear arrangement being rotatable about the pin shaft.15. A transmission according to claim 1, wherein said driven gearincludes teeth arranged to cooperate with teeth provided in said geararrangement.
 16. A transmission according to claim 15, wherein saidteeth are located on an opposite side of the driven gear from thesurface in which said annular concavity is provided.
 17. A transmissionaccording to claim 1, wherein said gear arrangement comprises at leasttwo gears disposed on opposite sides of the axis of rotation of thedrive shaft and having an aligned axis of rotation.
 18. A transmissionaccording to claim 17, wherein said at least two gears are pinion gears.19. A transmission according to claim 17, wherein said wheel-drivingoutput comprises a gear which engages the said gear arrangement.
 20. Atransmission according to claim 17, further comprising a connectorelement associate with each of said at least two gears, said connectorelement being joined to the wheel-driving output element to translaterotation of the gear arrangement about the axis of rotation of the driveshaft to rotation of the wheel-driving element.
 21. A transmissionaccording to claim 20, wherein said at least two gears are pinion gearsand wherein said connector elements are pins each having a shaftpositioned along the aligned axis of rotation of said at least twogears, the said at least two gears being rotatable about theirrespective pin shafts.